1. Field of the Invention
The invention relates to testing assisted position location capable devices. In particular, the invention relates to a position determination entity simulator used in testing assisted position location capable devices.
2. Description of the Related Art
Recently there has been a great deal of interest in determining the location of mobile devices. One area that is of particular interest is the ability to determine the location of cellular phone users in certain circumstances. For example, the Federal Communications Commission (FCC) of the U.S.A. has mandated that the location of a cellular telephone user be determined automatically when the user dials 911. In addition to the FCC mandate, it is envisioned that other applications that can take advantage of knowing a users"" location will be developed.
Various techniques have been used to determine the location of a mobile unit. For example, the Global Positioning System (GPS) is a satellite system that provides users equipped with a GPS receiver the ability to determine their location anywhere in the world. A GPS receiver normally determines its location by measuring the relative times of arrival of signals transmitted simultaneously from multiple GPS satellites.
Each GPS satellite transmits a microwave carrier signal that is xe2x80x9cspreadxe2x80x9d by a repeating pseudo random noise (PRN) code. The PRN code of each satellite is unique to that satellite, and all PRN codes repeat with the same duration. In addition, the spreading of the carrier signal used by all GPS satellites is synchronized to begin at the same time, corresponding to GPS time. The microwave carrier signal is also modulated by a 50 Hz signal that contains data describing the satellite orbits, clock corrections, and other system parameters. The GPS satellite positioning data, as well as data on clock timing, is commonly referred to as xe2x80x9cephemerisxe2x80x9d data.
Typically, a GPS receiver is able to produce, or has stored in memory, replicas of PRN codes used by the GPS satellites. The receiver shifts the PRN replica in time until there is correlation with the PRN code transmitted by the satellite and received at the GPS receiver. The offset in time corresponding to when there is a correlation represents the time of arrival (TOA) of the satellite PRN at the receiver. The TOA is proportional to the distance between the satellite and the receiver, offset by any difference between the receiver clock and GPS time. The TOA is commonly referred to as the pseudo-range. To be able to solve for the receiver location, the GPS receiver measures the pseudo-ranges to multiple satellites (typically four) to solve for x, y, and z position and to correct timing errors between the receiver clock and GPS time. In addition to the pseudo-range measurements, the receiver demodulates the emphemeris data to allow estimation of the location of the satellites when a pseudo-range measurement is made. Knowing the location of the satellites and the relative range to each satellite allows the receiver location to be estimated through a trilateration process.
The process of searching for and acquiring GPS signals, reading the ephemeris data for a multiplicity of satellites and estimating the location of the receiver from this data is time consuming, often requiring several minutes. In many cases, this lengthy processing time is unacceptable and, furthermore, greatly limits battery life in micro-miniaturized portable applications.
Several techniques have been attempted to reduce the time needed to acquire the GPS data used in location estimation. One such technique that has been developed by the wireless communication industry is the TIA/EIA IS-801-1 standard entitled xe2x80x9cPosition Determination Service Standards for Dual Mode Spread Spectrum Systemsxe2x80x9d, incorporated herein in its entirety. The IS-801-1 standard includes definitions for messages that are communicated between a mobile unit and a network infrastructure, such as a cellular network, to reduce the time needed to acquire the GPS data. The mobile unit may comprise, for example, a GPS-enabled cellular telephone. The network infrastructure may include a Position Determination Entity (PDE) that assists the mobile unit acquiring the GPS data. For example, when it is desired to determine the location of the mobile unit, the PDE may communicate assistance data to the remote unit to improve the mobile unit""s acquisition of the GPS data. Such assistance data may include, for example, the PRN code of the GPS satellites that are most likely to be in the view of the mobile unit, Doppler information, including Doppler search window size, and PRN code phase search window.
Another well-known position location technique is Advanced Forward Link Trilateration (AFLT). The AFLT technique is based on measuring time-of-arrival differences between terrestrial base station signals. In the case of a CDMA wireless network, these measurements are called pilot phase measurements. Whenever the mobile device is able to detect signals from three different base station locations, one of which is likely to be the serving base station, the mobile device""s position can be determined.
It is possible that at a particular location, the mobile device is neither able to detect signals from at least four GPS satellites nor able to detect signals from at least three base stations. In this case, neither the GPS nor the AFLT technique alone would give a position solution. A third technique, commonly referred to as a xe2x80x9cHybridxe2x80x9d technique, combines the GPS and AFLT measurements. The hybrid technique may still give a position solution even in the case in which less the required number of satellites are available. When the mobile device communicates with a GPS synchronous cellular network, such as an IS-95 or IS-2000 standards compliant CDMA network, the Hybrid technique has the additional advantage of further reducing the required minimum number of measurements. Both the AFLT and Hybrid techniques are supported by the IS-801-1 standard, which defines applicable assistance messages to be sent by the PDE to the mobile device.
Presently, various vendors are developing PDEs to comply with the IS-801-1 standard. However, even if two PDEs from different vendors both meet the IS-801-1 standard, the assistance data provide by the two PDEs may be different. Differences in the assistance data provided to a mobile unit may affect the performance of the mobile unit in acquiring GPS data. For example, it may take longer for a mobile unit to acquire the GPS data with the assistance data provided by one vendor""s PDE than with another vendor""s PDE. Most mobile units, however, are optimized for operation with a specific vendor""s PDE. The published performance specifications of a mobile unit may relate to operation with the PDE for which the mobile unit has been optimized.
Variations in PDE performance make it difficult to test and compare the performance of various mobile units. For example, if a single vendor produces both PDEs and mobile units, the PDE and mobile units may achieve a satisfactory level of performance together. However, the same PDE or mobile unit may not achieve satisfactory performance when operating with a mobile unit or PDE produced by a different vendor. As it is anticipated that there will be many different manufacturers of PDEs and mobile units, variations in performance when different combinations of PDEs and mobile units interact can reduce the overall effectiveness in estimating the location of the remote unit. This can result in very severe consequences, particularly in an emergency, or 911, situation.
Due to these and other problems, there needs to be a standard technique and apparatus that facilitates testing of mobile unit performance when acquiring GPS data for estimating the mobile unit""s location.
A method and apparatus for testing assisted position location capable devices are provided. One aspect is providing a position determination entity (PDE) simulator that is in communication with a base station simulator. The base station simulator simulates one or more base stations. The disclosed method includes connecting an assisted position location capable device under test to the base station simulator, a global positioning system (GPS) simulator, and initiating a test sequence wherein the device under test receives a set of predetermined GPS signals. At a desired time, the device under test (DUT) requests assistance data from the base station simulator and the base station simulator requests assistance data from the PDE simulator, wherein the PDE simulator provides data that is independent of the GPS simulator data to the base station, and the base station transfers the PDE data to the DUT. The PDE data may be a set of predetermined responses to any one of a plurality of requests.
Another aspect of a method for testing assisted position location capable devices includes (1) providing a position determination entity (PDE) simulator that is in communication with a base station simulator simulating one or more base stations, (2) connecting an assisted position location capable device under test to the base station simulator and a global positioning system (GPS) simulator, and (3) initiating a test sequence. During the test sequence, the PDE simulator provides assistance data and a request for the device under test to make pseudo-range measurements or pilot phase measurements or both, and wherein the device under test receives the assistance data and the request and, using the assistance data, makes pseudo-range measurements or pilot phase measurements or both and provides the measurement results to the base station simulator. The PDE data may be a set of predetermined responses indexed by elapsed test time.
Another aspect of testing assisted position location capable devices in accordance with the invention includes providing a position determination entity (PDE) simulator that is in communication with a base station simulator simulating one or more base stations and connecting an assisted position location capable device under test to the base station simulator and a global positioning system (GPS) simulator and initiating a test sequence. In the test sequence, the PDE simulator provides assistance data and a request for the device under test to make a location measurement, and the device under test receives the assistance data and the request and, using the assistance data, makes a location measurement and provides the location measurement to the base station simulator. The PDE data may be a set of predetermined responses indexed by elapsed test time.
A position determination entity (PDE) simulator constructed in accordance with the invention includes a controller configured to receive assistance requests and to output assistance responses, and operates with a database populated with predetermined assistance responses corresponding to a set of assistance requests. An appropriate response is selected from the database in accordance with the received type of assistance request and the elapsed test duration. The assistance responses may correspond to GPS or AFLT data.